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Feeding on the roof of the world: the first gut content analysis of very high altitude Plecoptera
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Feeding on the roof of the world: the first gut content analysis
of very high altitude Plecoptera
Angela Boggero, Tiziano Bo, Silvia Zaupa, Stefano Fenoglio*
Boggero, A., Bo, T., Zaupa, S. & Fenoglio, S. 2014: Feeding on the roof of the world: the first gut content analysis of very high altitude Plecoptera. — Entomol. Fennica 25: 00–00.
The biology of Plecoptera from high altitude Himalayan freshwaters is almost unknown. Very few and sporadic studies have been devoted to these insects, and exclusively with a taxonomic approach. We provide information on the feeding of Capnia nymphs from three lakes localized above 4800 m a.s.l. (NE Nepal). Nymphs from these high altitude lakes feed mainly on fine detritus, acting as col-lector-gatherers, with the accidental ingestion of mineral matter, mostly in larger specimens. It is likely that the harsh environmental conditions in our study area create an environment unfavorable to both the allochthonous input of coarse par-ticulate organic matter (such as terrestrial leaves) and the autochthonous input re-lated to aquatic primary productivity, so that these nymphs feed on small organic particles that originates mainly from the catchment.
A. Boggero & S. Zaupa, National Research Council (CNR), Institute of Ecosys-tem Study, Verbania Pallanza, Italy
T. Bo & S. Fenoglio, Dipartimento di Scienze e Innovazione Tecnologica (DISIT), Università del Piemonte Orientale, Alessandria, Italy; *Corresponding author’s e-mail: fenoglio@unipmn.it
Received 8 April 2014, accepted 13 May 2014
1. Introduction
Studies dedicated to the trophic ecology of aquatic insects have become a central element in modern aquatic entomology (Lancaster & Downes 2013). Expanding the knowledge about foraging of aquatic hexapods is crucial for de-scribing auto-ecological aspects of the dominant invertebrate group in inland waters, analyzing trophic webs, and better understanding functional dynamics of freshwater ecosystems (Monakov 2003).
Plecoptera, or stoneflies, constitutes a rela-tively small order of hemimetabolous insects, particularly adapted to the life in cold waters and for this reason mainly distributed in mountainous
systems (Fochetti & Tierno de Figueroa 2008). Among the most orophilous stonefly families, Capniidae includes 17 genera and 315 species with a mainly Holartic distribution (Fochetti & Tierno de Figueroa 2008). According to Merrit and Cummins (1996), members of the family Capniidae are generally considered shredders, mainly feeding on plant fragments and other coarse particulate organic matters (Fleituch 2013, Taylor & Chauvet 2014).
A conspicuous deal of attention has been de-voted to the study of various aspects of the lim-nology of high altitude Himalayan lakes (Pandit 1999), but interestingly, almost no data are avail-able about trophic ecology of the few aquatic in-sect taxa that inhabit these extreme ecosystems.
Accordingly, the aim of the present study is to provide the first data, as far as we know, about feeding habits of very high altitude stoneflies.
2. Material and methods
During 2008 and 2012 sampling campaigns of the Italian National Research Council (CNR), stonefly nymphs were collected from three high altitude lakes (> 4,800 m a.s.l.) in Sagarmatha National Park, in the North-Eastern region of Ne-pal. These Himalayan lakes do not have a proper name, but are identified by progressive numbers (Lake Cadastre Number, LCN). They are fed prevalently by perennial snow, glaciers, or direct runoff from precipitation, and are located in bas-ins where large areas are covered by glaciers, rocks, landslides and, in minor amount, alpine prairies (Tartari et al. 1998a,b). The main abiotic characteristics at the sampling time are reported in Table 1.
Sampling for chemical and biological analy-sis was performed using one litre polyethylene bottle at a lake depth of 50 cm, and kicking the lake sediment with a handle-net for a maximum of five minutes along the littoral. Sampling was carried out simultaneously in both occasions, in autumn, after the monsoon period. Chemical
samples were then stored in the dark at 4 °C until the laboratory analyses which were performed according to the methods described on the web site: http://www.idrolab.ise.cnr.it/. Biological samples were then fixed with 80% alcohol before being sieved, sorted, and identified to genus level. The extreme paucity of literature regarding Hi-malayan stoneflies and the fact that all specimens were in the immature stage prevented a deeper identification, but we are confident that the unici-ty of our study, realized at such elevate altitudes, justifies its interest.
Total length, pronotum width and metatho-racic femur length of the sampled nymphs were measured with a Nikon SMZ 1500 stereomicro-scope (0.10 mm accuracy). The measurements were standardized by placing each nymph be-tween two slides. Nymphal diet was determined through the gut content observation of the col-lected specimens. Each specimen was cleared af-ter introducing it in Hertwigs’ liquid and heating it in an oven at 65 ºC for 24 hours, following the methodology of Bello and Cabrera (1999), which is used in many studies of nymphal feeding of aquatic insects (e.g. Fenoglio et al. 2007, Bo et al. 2012). The percentage of the absolute gut content (at 40x) was estimated as the proportion of diges-tive tract occupied by dietary items. The reladiges-tive gut content (at 400x) was calculated by
measur-2 Boggero et al. • ENTOMOL. FENNICA Vol. 25
Table 1. Main abiotic characteristics of the study lakes*.
LCN 75* LCN 128* LCN 129*
Altitude (m a.s.l.) 4,839 5,090 5,240
Valley Nojimba Thyanmoche Thyanmoche
Map coord. (UTM W GS84)
latitude 3092496 3089787 3091945 longitude 469790 465110 465940 Lake surface (km2) 0.42 0.03 0.07 Conductivity (µS cm–1 ) 41.4 55.6 58.2 Temperature (°C) 8.0 6.0 4.0 pH 7.40 6.92 7.38 N-NH4 (µeq l–1 ) 0.0 0.0 0.0 N-NO3 (µeq l–1) 3.0 7.0 2.0 SO4 (µeq l–1 ) 131 334 333 Ca (µeq l–1) 329 395 429 Mg (µeq l–1 ) 51 87 92 Cl (µeq l–1) 1.0 2.0 1.0 Alk (µeq l–1 ) 262 161 202 Total P (µg P l–1) 6.0 4.0 4.0 Total N (µg N l–1 ) 70 150 70
ing the area of gut content occupied by each di-etary item. Mean, standard deviation, minimum and maximum were calculated. Data were ana-lyzed using PAST software (Hammer et al. 2001): Pearson correlation was used for continu-ous variables (nymph measures) while Spearman test was employed to find a correlation between
nymph size and gut content (a categorical vari-able).
3. Results
All stonefly nymphs belonged to the genus
Capnia, family Capniidae. A total of 46 stonefly
Fig. 1. Relationship be-tween total body length and pronotum width in high altitudeCapnia nymphs.
Fig. 2. Relationship be-tween total body length and amount (%) of in-gested mineral matter in high altitudeCapnia nymphs.
nymphs were measured and processed for gut content analyses (n = 30 from Lake LCN 75, n = 11 from Lake LCN 128 and n = 5 from Lake LCN 129). Mean (± S.D.) total length was 3.89 mm (± 0.2 mm).
Among the three morphometric parameters measured, we detected a significant correlation between total length and pronotum (r = 0.88, P < 0.001, Fig. 1), total length and femur (r = 0.83, P < 0.001), femur and pronotum measures (r = 0.75, P <0.001). For these reasons, we utilized the total length as an indicator parameter of nymph size.
Forty-one nymphs had some content in their guts and fine detritus was the fundamental com-ponent in the guts of these high altitude Capniidae nymphs (Table 2). Diatoms, pollen, CPOM (coarse particulate organic matter) and fungi were present in the diet in very low quantities. Mineral matter constituted a considerable percentage of the gut contents, but this was probably due to in-cidental ingestion. No significant correlation with body size was found for the food items except the amount of mineral matter being positively corre-lated with total length (rs = 0.65, P < 0.001, Fig. 2).
4. Discussion
As mentioned above, Capniidae are among the most limnophilous Plecoptera, often inhabiting ponds and lakes. An exceptional example is pro-vided by Capnia lacustra Jewett, 1965 which spends its entire life, including the adult stage, in the deep waters of Lake Tahoe, but many other
Capniidae species inhabit lentic systems too (Donald & Patriquin 1983). Moreover, Capniidae are “an icon for cold adaptation” (Pescador et al. 2000). Brittain (1974) reported that Capnia atra Morton, 1896 occurs even in the most extreme lentic habitats in Norway and has the capacity to rapidly colonize even lakes recently created by glacier retreat. For these reasons, it is not surpris-ing that nymphs of this family are able to develop in very high altitude Himalayan lakes. At present, the few and sporadic studies that regarded the presence of these stoneflies in Himalaya (e.g., Kimmins 1946, Kawai 1968, Harper 1977, Zwick & Sivec 1980) were exclusively focused on taxonomic aspects.
Recently, López-Rodríguez and Tierno de Figueroa (2008) reported a greater variation in food resources among Capniidae nymphs than previously known. Moreover, Bo et al. (2013) re-ported that Capnia bifrons (Newman, 1838) shifts from being a collector-gatherer to a shred-der along its nymphal growth. Our results show that in high altitude Himalayan lakes Capniidae nymphs are mainly collector-gatherers feeding on fine organic detritus. These freshwater sys-tems are located above the tree-line, where allochthonous inputs of organic matter is ex-pected to be extremely low. Moreover, these lakes have cold and ultra-oligotrophic waters, so that even autochthonous inputs (i.e., productivity of macrophytes, phytoplankton and ephilitic algae) are particularly low. For these reasons, we can hy-pothesize that Capniidae nymphs can only feed on small organic particles mainly derived from the catchment. Nymphs collect fine detritus di-rectly from the substratum, and we can assume
4 Boggero et al. • ENTOMOL. FENNICA Vol. 25
Table 2. Gut contents of the Capniidae nymphs as proportion (%) of the gut volume filled with food (n = 46) and proportions of different components in the total food volume in cases with food in the gut (n=41, i.e. 5 guts were empty)
Mean SD Minimum Maximum
% absolute content 43.7 33.4 0.00 90.0 % detritus 81.8 29.7 0.00 100.0 % diatoms 0.41 1.34 0.00 5.00 % pollen 0.24 1.56 0.00 10.0 % CPOM* 0.20 0.90 0.00 5.00 % hyphae 0.05 0.31 0.00 2.00 % mineral matter 7.27 10.3 0.00 40.0
that larger nymphs ingest more mineral matter be-cause of the larger dimension of their mouthparts.
Acknowledgments. This study was carried out within the
framework of the Ev-K2-CNR “Scientific and Technolog-ical Research in Himalayas and Karakorum” Project with support from the Ev-K2-CNR Committee and in collabo-ration with the Royal Nepal Academy of Science and Technology (RONAST). The research was also made pos-sible thanks to contributions from the Italian National Re-search Council (CNR) and the Italian Ministry of Foreign Affairs. We thank R. Fochetti for bibliographic help. We thank also Manuel Jesús López Rodríguez and an anony-mous reviewer for their useful suggestions to improve the manuscript.
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